Liquid galley refrigeration system for aircraft

ABSTRACT

The liquid galley refrigeration system for cooling food carts for aircraft employs an intermediate working fluid to transfer heat from one or more food carts to one or more remote chillers, allowing the carts and chillers to be advantageously distributed in the aircraft. A plurality of heat exchanges effect a cooling of the carts wherein heat from the food cart is first transferred to a first airflow; heat from the first airflow is then transferred to an intermediate working fluid that is circulated between a location immediately adjacent the food carts and a remote chiller; heat from the intermediate working fluid is subsequently transferred to the chiller working fluid; and finally, heat from the chiller working fluid is expelled. While the chiller working fluid undergoes a phase change in order to transfer heat from the intermediate working fluid to the cooling air, the intermediate working fluid remains in its liquid phase throughout its circulation. A recirculation pump circulates the intermediate working fluid through a distribution system that may link a plurality of chillers to a plurality of food carts, and the temperature of the food carts is regulated by a combination of controls.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to transport aircraft galley systems, andmore particularly, to systems to cool food carts prior to service by thecabin attendants.

[0003] 2. Description of Related Art

[0004] Aircraft galley systems for modern transport aircraft incorporatefood carts which are cooled to prevent food spoilage prior to use by thecabin attendants for distribution of food to the passengers. These foodcarts have in the past been interfaced with cold air supply systems inthe galley designed to cool the interiors of the food carts. Such coolair distribution systems were generally co-located with the balance ofthe galley and interface to the food carts by means of gasketsconnecting the food carts to a plenum containing the cool air.

[0005] As space in modern aircraft has become more at a premium and moreefficient means of cooling the carts has become necessary, there hasemerged a need for alternatives to such systems. Furthermore, recent FDArulings have lowered the required temperature at which the interior ofthe food carts has to be kept in order to prevent food spoilage.Additionally, it has become more desirable to remove refrigerationequipment from the galley compartment and to find other means toproperly cool the food carts without locating the entire refrigerationsystem in the galley area. In order to be compatible with moderntransport aircraft requirements, it has become important to have anincreased degree of safety and modularity for any aircraft systemincorporating electronics or electric pumps, and it would beparticularly desirable to locate at least a portion of such systemsoutside of the cabin area of the aircraft. In any event, it is importantthat any system that interfaces with either food or the cabin area isnon-toxic and can be configured to provide a wide range of coolingcapacity as a function of the food and food carts that are to beinterfaced with such a system. The present invention satisfies these andnumerous other requirements for transport aircraft.

SUMMARY OF THE INVENTION

[0006] The present invention overcomes the shortcomings of previouslyknown systems for cooling food carts in aircraft. The system of theinvention serves to not only remove the bulk of the refrigeration systemfrom the galley area but also obviates the need to accommodate bulky airducts that would supply cooled air from refrigeration stations directlyto the carts. Additionally, the system allows low temperatures to bereadily achieved in a very controllable manner.

[0007] In general terms, the invention employs an intermediate workingfluid to transfer heat from a cart or carts to a remote chiller orchillers. In a presently preferred embodiment, the components of thesystem may be advantageously positioned in the aircraft and do not haveto be contained in a single location. More specifically, the inventionutilizes a plurality of heat exchangers to effect a cooling of the cartswherein heat from the food cart is first transferred to an airflow; heatfrom the airflow is then transferred to an intermediate working fluidwhich is circulated between a location immediately adjacent the foodcarts and a remote chiller; heat from the intermediate working fluid issubsequently transferred to the chiller working fluid; and finally, heatfrom the chiller working fluid is expelled to ambient air.

[0008] While in the currently preferred embodiment, the chiller workingfluid undergoes a phase change in order to transfer heat from theintermediate working fluid to the ambient air, the intermediate workingfluid typically remains in its liquid phase throughout its circulation.A recirculation pump serves to circulate the intermediate working fluidthrough a distribution system that may link a plurality of chillers to aplurality of food carts. An expansion tank accommodates the expansionand contraction that the intermediate working fluid undergoes during itscirculation. Each of the chillers cycles the associated chiller workingfluid between a condenser and evaporator in a conventional mannerwhereby an expansion valve is relied upon to control the phase changetherebetween.

[0009] The temperature of the food cart is regulated by a combination ofcontrols. The speed of a fan circulating air flowing over the heatexchanger for the intermediate working fluid and directing the aircooled in this manner through the food cart may be varied so as toinfluence the rate of heat transfer between the food cart and theintermediate working fluid. A variable flow valve may be used to controlthe flow of intermediate working fluid to each cart, while the flowvelocity of the intermediate working fluid circulating in the entiredistribution system may be controlled by varying the speed of therecirculation pump. Finally, each of the chillers may be turned on oroff depending upon the temperature of the intermediate working fluidreturning from the food carts. Temperature sensors and pressure sensorsare positioned throughout the system to monitor these parameters atappropriate locations in order to allow the operation of the overallsystem to be properly controlled by the use of electronic controls suchas programmable industrial controllers. (PIDs)

[0010] Other features and advantages of the present invention willbecome more apparent from the following detailed description of thepreferred embodiments in conjunction with the accompanying drawings,which illustrate, by way of example, the operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic diagram illustrating a general overview ofthe galley refrigeration system for aircraft according to the invention.

[0012]FIG. 2 is a schematic diagram illustrating the general designparameters of the galley refrigeration system for aircraft according tothe invention.

[0013]FIG. 3 is a schematic diagram of a distributed version of thegalley refrigeration system for aircraft according to the invention.

[0014]FIG. 4 is a schematic diagram of a first version of a layout of adistributed galley refrigeration system for aircraft according to theinvention.

[0015]FIG. 5 is a schematic diagram of a second version of a layout of adistributed galley refrigeration system for aircraft according to theinvention.

[0016]FIG. 6 is a schematic diagram of a third version of a layout of adistributed galley refrigeration system for aircraft according to theinvention.

[0017]FIG. 7 is a schematic diagram of a fourth version of a layout of adistributed galley refrigeration system for aircraft according to theinvention.

[0018]FIG. 8 is a schematic diagram of an electronic control system forcontrolling the galley refrigeration system for aircraft according tothe invention.

[0019]FIG. 9 is a schematic diagram of a galley air cooling unit of thegalley refrigeration system for aircraft according to the invention.

[0020]FIG. 10 is a signal block diagram of an electronic control systemfor controlling the galley refrigeration system for aircraft accordingto the invention.

[0021]FIG. 11 is a diagram of a control panel for operation of thecontrol system for controlling the galley refrigeration system foraircraft according to the invention.

[0022]FIG. 12 is an overall thermodynamic chart of the galleyrefrigeration system for aircraft according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention is directed to a system for refrigeratingfood carts within an aircraft galley system. Generally, the systemincludes a set of remote chillers which remove heat from a distributedliquid refrigerant system, which in turn removes heat from one or morefood carts to refrigerate the food carts. The entire system iselectronically monitored and controlled to provide a sufficientlychilled environment within a potentially large number of food carts.

[0024] More specifically, the present invention includes threedistributed refrigeration subsystems, and an electronic controlsubsystem for monitoring and controlling the refrigeration subsystems.The first refrigeration subsystem includes at least one remote chiller,the second refrigeration subsystem includes at least one galley aircooling unit, and the third refrigeration subsystem includes at leastone recirculation unit.

[0025] Each remote chiller constitutes a self-contained refrigerationunit, which serves to remove heat from a liquid refrigerant, referred toas the intermediate working fluid. The intermediate working fluid isthen distributed to the second refrigeration subsystem. The galley aircooling units each include a galley cart and a galley plenum. Thechilled intermediate working fluid is distributed into and exits from aheat exchanger within the galley plenum. A blower or fan within theplenum blows air over the exchanger and through the galley cart. In thismanner, the galley cart may be continually flushed with air chilled bythe galley plenum heat exchanger.

[0026] Upon exiting the galley plenum the intermediate working fluid isdistributed to the third refrigeration subsystem. Each recirculationunit may include one or more liquid pumps and expansion tank oraccumulator. The one or more pumps of the recirculation units pressurizethe intermediate working fluid for redistribution to the remotechillers. The accumulators of the recirculation units allow for thestorage and thermal expansion of the intermediate working fluid.

[0027] The electronic control subsystem is also a distributed systemwhich may monitor and control individual components of eachrefrigeration subsystem. Individual electronic devices may be used tomonitor and control the temperature within each galley cart. The galleyair cooling units may include a control valve to vary the amount ofliquid refrigerant entering the galley plenum. The electronic devicesmonitoring the temperature of the air in the galley cart may be used toadjust the control valve. These same electronic devices may also be usedto turn the fan in the galley plenum on and off.

[0028] Other electronic devices may be used to monitor and control therecirculation units. These electronic devices monitor and control therecirculation units. These electronic devices may also be configured tomonitor the pressure and volume within the expansion tank. Therecirculation units may be controlled by turning the pumps on and off orby varying the speeds by which the pumps operate.

[0029] Other electronic devices may also be used to monitor and controlthe remote chillers. By monitoring the pressure and temperature withinthe remote chiller the electronic devices can appropriately determinewhich remote chillers to operate at different times.

[0030] The electronic subsystem may be powered by the aircraftelectrical power systems. The electronic subsystem may also include anynumber of display systems and interfaces for control by the crew. Anoverall control system may operate each individual electronic device.

[0031] The entire system and each individual component should beconfigured for operation within the unique environment presented bytransport aircraft. Equipment used on commercial aircraft must meetstrict requirements. In addition to maintaining food at safetemperatures, general aircraft operating requirements must be met. Thesize and weight of the system must be kept to a minimum. The reliabilityand ease of maintenance are key economic considerations. Firesuppression, non-toxicity and electromagnetic interference (EMI)shielding are key safety considerations. The present invention allowsfor these concerns, and others, to be met satisfactorily.

[0032] As depicted in FIG. 1, several components combine to form agalley air cooling unit 18. A galley cart 20 is typically stored withina galley plenum 22 while storing food. To safely store the food the airwithin the galley cart must be stored at or below a specifictemperature. For example, 39° F. (4° C.) is the temperature required bycertain agencies. The galley plenum is equipped with gaskets to form anair tight seal with the galley cart. Preferably the galley plenum isequipped with a blower 24 or fan which circulates air throughout thegalley cart and over at least one heat exchanger 26 within the galleyplenum. Ducts 25 between the galley cart and the galley plenum directthe flow of air across the stored food.

[0033] The heat exchanger 26 within the galley plenum 22 may include aplate and fin configuration optimized for removing heat from passingair. The present invention contemplates the exchange of thermal energybetween ambient air and a liquid refrigerant, also referred to as a heattransfer fluid, or the intermediate working fluid 27. A known heattransfer fluid having appropriate thermal and physical properties foruse with the present invention is a fluorinated heat transfer fluid soldunder the trademark GALDEN®HT 135. GALDEN®HT 135 is a perfluoropolyetheror PFPE fluid sold by the Ausimont Montedison Group, although othersimilar heat transfer fluids may also be suitable.

[0034] A large number of the galley carts 20 (e.g. 45) may be requiredon a single aircraft. In a currently preferred embodiment, each galleycart may require a thermal exchange of approximately 750-1000 BTUs perhour. The corresponding air flow requirement of each galley cart in suchan arrangement would then be approximately 72 cubic feet per minute. Thecorresponding fluid flow through each heat exchanger 26 would beapproximately 0.64 gallons per minute (using GALDEN®HT 135). Systems inaccordance with the present invention may be designed to meet theserequirements for as many galley carts as are used on an aircraft.

[0035] A proportional flow valve 28 may be used to control the flow ofthe intermediate working fluid 27 from each heat exchanger 26 within thegalley plenum 22. It is also contemplated that a single proportionalflow valve may control the flow of fluid into two or more heatexchangers. One method of controlling the temperature of the air withinthe galley cart 20 is to electronically manipulate the proportional flowvalve so as to regulate the flow of fluid into the heat exchanger.

[0036] As depicted in FIG. 1, the source of the chilled intermediateworking fluid is at least one remote chiller unit 30. After exiting theheat exchanger 26 within the galley plenum 22 the intermediate workingfluid is no longer chilled. The unchilled intermediate working fluid isreturned to the chiller unit via the valve 28, cooled, and redistributedthroughout the system by at least one recirculation unit 32.

[0037] As depicted schematically in FIG. 2, a simple system conformingto the present invention may consist of a remote chiller unit 30 and aredistribution unit 32 refrigerating several galley carts 20. As anexample, the liquid chiller unit may be configured as a vapor cyclerefrigeration unit. In such a unit, a compressor 34 (a pump or othermachine that increases the pressure of a gas) may be powered by theaircraft's electrical system. Preferably, a rotary-type compressor isused to compress low temperature and pressure vapor into hightemperature and pressure super-heated vapor. The material to form thisvapor is also a refrigerant and may be referred to as a chiller workingfluid 35 (See FIG. 1). A known material which has appropriate thermaland physical properties for use with the present inventions as thechiller working fluid is a hydrofluorocarbon refrigerant such as thatsold under the name HFC-134a available from DuPont, or sold under thename MEFOREX 134a, or HT 134a, available from Ausimont, as a replacementfor CFC12, although other similar refrigerants may also be suitable.

[0038] From the compressor 34, the chiller working fluid 35 flows into acondenser 36. The condenser is preferably configured as a tube-fin heatexchanger to maximize heat rejection. From the condenser, the chillerworking fluid flows through an expansion valve 38 into an evaporator 40.The evaporator is preferably configured as a plate-fin heat exchanger tomaximize heat absorption.

[0039] Associated with the evaporator 40 is an expelling heat exchanger42. The intermediate working fluid 27 flows through the expelling heatexchanger. The association of the evaporator with the expelling heatexchanger forms a chiller unit heat exchanger 43 (see FIG. 1) andenables a thermal exchange between the intermediate working fluid andthe chiller working fluid 35 without the fluids ever mixing. As thechiller working fluid passes through the evaporator 40, back into thecompressor 34, it draws heat from the expelling heat exchanger and theintermediate working fluid.

[0040] A remote chiller unit 30 in accordance with this invention may berequired to maintain a required low temperature in several galley carts20. As an example, the total heat rejection required of a single remotechiller unit may be 18,000 BTUs per hour. This would require a flow rateof the intermediate working fluid 27 of 4.6 gallons per minute (usingGALDEN® HT135). A corresponding flow rate through the condenser would be700 cubic feet per minute at 3.5 inches H₂O pressure (using HT-134a).This could be supplied by a condenser blower wheel operating at 5,750revolutions per minute. Further requirements of such a remote chillerunit 30 may be an air venting fan as well as a mechanical bypass valve.

[0041] The unchilled intermediate working fluid 27 flows out of the heatexchanger 26 in the galley plenum 22 and is redistributed to a liquidpump 44 in at least one recirculation unit 32. The liquid pump may beconfigured as a turbine impeller pump which delivers relatively highpressure at relatively low flow rates. The liquid pump should beentirely sealed to prevent any leakage of the intermediate workingfluid. The liquid pumps supply all the force required to maintain thecirculation of the intermediate working fluid through the components ofthe system.

[0042] Within the recirculation unit 32, the intermediate working fluid27 flows into an expansion tank 46. The expansion tank functions as anaccumulator and a reservoir for the intermediate working fluid. Theexpansion tank allows for thermal expansion of the intermediate workingfluid. Preferably, throughout the entire process, the intermediateworking fluid remains in the liquid state.

[0043] Each recirculation unit 32 may gather intermediate working fluid27 from several galley air cooling units 18. Each recirculation unit mayalso provide intermediate working fluid to several remote chiller units30. As an example, the flow rate through a single recirculation unit maybe 10 gallons per minute. The recirculation units may also be requiredto provide a pressure differential of 100 pounds per square inch in theintermediate working fluid.

[0044] As depicted in FIG. 3, systems conforming to the presentinvention may be distributed systems. That is, a plurality of remotechiller units 30 may combine to remove heat from a plurality of galleycarts 20, and the entire system may be continually recirculated by atleast one recirculation unit 32. This permits the remote chiller units30 and recirculation units 32 to be located at an accommodating distancefrom the galley carts 20. Because of the limited space available oncommercial transport aircraft this can be very advantageous.

[0045] To circulate the intermediate working fluid 27 throughout thedistributed system, a network of ducts connects the individualcomponents. Supply ducts 48 are configured to distribute the chilledintermediate working fluid to the galley air cooling units 18.Redistribution ducts 49 are configured to route the unchilledintermediate working fluid to the liquid pumps 44. Return ducts 50 areconfigured to distribute the unchilled intermediate working fluid to theremote chiller units 30.

[0046] FIGS. 4-7 depict various configurations of the present invention.The differing configurations of various commercial aircraft require agreat deal of flexibility in placement of remote chiller units 30 andrecirculation units 32. As the galley carts 20 may be distributed invarious galleys throughout the aircraft, the supply ducts 48,redistribution ducts 49 and return ducts 50 may run potentiallythroughout the entire aircraft. The present invention allows each of thecomponents of the refrigeration system to be distributed toaccommodating locations within the galleys or nearby.

[0047] As depicted in FIG. 8, the present invention may also include acomprehensive electronic subsystem to monitor and control thedistributed refrigeration system. A galley cart control device 52 may beassociated with each galley air cooling unit 18. An air outlettemperature sensor 54 and an air supply temperature sensor 56 may eachprovide input to the galley cart control device. The galley cart controldevice may then turn on or off the blower 24 as well as control theoutput of the proportional flow valve 28.

[0048] A chiller unit monitoring device 58 may be associated with eachremote chiller unit 30. By means of a pressure transducer 60, athermo-sensor 62 and a current sensor 64 the chiller unit monitoringdevice may measure the function of the remote chiller unit. If needed,the chiller unit monitoring device could shut down the remote chillerunit.

[0049] A system monitoring and control device 66 may be associated witheach recirculation unit 32, or may be associated with the system as awhole. The system monitoring and control device may monitor the volumeand pressure within each expansion tank 46 as well as the functioning ofthe liquid pumps 44. Furthermore, the system monitoring device maymonitor the temperature and pressure of the intermediate working fluid27 at various locations within the system. The system monitoring andcontrol device may also receive input from the chiller unit monitoringdevices 58 and the galley cart control devices 52. With thisinformation, the system monitoring and control device may control thefunctioning of each and every electronic and refrigeration component ofthe entire system.

[0050] As depicted in FIG. 9, the galley cart control device 52, maycontrol the temperature of the air in the galley cart 20 by regulatingthe flow of the intermediate working fluid 27 into the heat exchanger 26within the galley plenum 22. The air supply temperature sensor 56measures the temperature of the cold supply air and relays thatinformation to the galley cart control device. In order to ensure thatthe cold supply air remains near a specified temperature (e.g. 30° F.(−1° C.)) the galley cart control device can increase or decrease theflow of intermediate working fluid by controlling the proportionalcontrol valve 28. As the flow of the intermediate working fluid into theheat exchanger increases the temperature of the supply air will decreaseand vice versa. The galley control device may also monitor thetemperature of the intermediate working fluid at various locations orthe temperature of the air returning to the heat exchanger. Furthermore,a differential pressure gauge 59 on the supply ducts 48 and a flow meter61 on the redistribution ducts 49 may provide additional informationabout the flow of intermediate working fluid into and out of the galleyair cooling unit 18. The galley cart control device could use thisfurther information to more efficiently regulate the proportional flowvalve or to turn the blower 24 on and off.

[0051] As depicted in FIG. 10 the components of the electronic subsystemmay be interrelated via the system monitoring and control device 66 alsoreferred to as the recirculation unit with control logic. That is, thesame electronic device used to monitor and control the recirculationunit 32 may be programmed to control the overall functioning of theentire system. This may include such functions as malfunction detectionand providing maintenance information. Each galley cart control device52 and chiller unit monitoring device 58 may be configured to sendsignals to the system monitoring and control device relaying informationabout the status of the galley air cooling units 18 and remote chillerunits 30. In turn, the system monitoring and control device could sendsignals back to the galley cart control device and chiller unitmonitoring device instructing the devices on how to control each galleyair cooling unit and remote chiller unit.

[0052] As depicted in FIG. 11, at least one display 70 may be includedwith the electronic subsystem. The display enables crew interface withthe refrigeration system. A set of lights indicates the status of thevarious components. A set of switches may permit crew control of thevarious components. The display may be electronically controlled by thesystem monitoring and control device 66.

[0053]FIG. 12 depicts a thermodynamic chart showing the functioning ofthe refrigeration subsystems. The information provided by the chart isexemplary of a system in accordance with the present invention. Thechart depicts the refrigeration process as a series of heat exchangesbetween the various fluids involved in the process.

[0054] It will be apparent to those of skill in the art that theexemplary systems described in this detailed description conform to theinvention described. It will also be apparent to those of skill in theart that various modifications may be made to the exemplary systemswhile remaining within the scope of the invention. Thus, the inventionis not intended to be limited to the examples described herein. Thescope of the invention is described and limited only by the followingclaims.

What is claimed is:
 1. A cooling system for use on aircraft, comprising:an onboard food cart; a chiller remotely located with respect to saidfood cart; and a first working fluid, wherein said first working fluidis in thermal communication with said food cart, in thermalcommunication with said remote chiller and in circulation there betweenand wherein said first working fluid remains in a liquid phase at alltimes.
 2. The system of claim 1, further comprising an expansion tankfor accommodating any expansion or contraction of said first workingfluid.
 3. The system of claim 1, further comprising a valve forcontrolling the circulation of said first working fluid to said foodcart.
 4. The system of claim 1, further comprising additional remotelylocated chillers, wherein said working fluid is in thermal communicationwith each of said additional remotely located chillers and incirculation therebetween.
 5. The system of claim 1, further comprisingadditional onboard food carts, wherein said working fluid is in thermalcommunication with each of said additional food carts and in circulationtherebetween.
 6. The system of claim 5, further comprising a valveassociated with each food cart for individually controlling thecirculation of said working fluid to each said food cart.
 7. The systemof claim 1, further comprising a pumping system configured to allow therate of circulation of said first working fluid to be varied.
 8. Thesystem of claim 1, wherein said chiller includes a recirculating secondworking fluid and further comprising a first heat exchanger fortransferring heat from said first working fluid to said second workingfluid.
 9. The system of claim 8, further comprising a second heatexchanger for transferring heat from air that is in contact with saidfood cart to said first working fluid.
 10. The system of claim 9,further comprising a circulation fan for circulating said air withinsaid food cart.
 11. A system for cooling of onboard food carts onaircraft, comprising: a first working fluid; a second working fluid; afirst heat exchanger for transferring heat from said first working fluidto said second working fluid; a first pump for circulating said firstworking fluid through said first heat exchanger and through fluidconduits to a second heat exchanger; an expansion tank for accommodatingany expansion or contraction of said first working fluid; a second pumpfor circulating said second working fluid through said first heatexchanger and through fluid conduits to a third heat exchanger; a blowerfor blowing air through said second heat exchanger to cool said air; andducts to direct said cooled air into a food cart.
 12. The system ofclaim 11, wherein said first working fluid undergoes no phase change atany time.
 13. The system of claim 12, wherein said first working fluidremains in a liquid phase at all times.
 14. The system of claim 11,further comprising a valve for controlling the flow of said first fluidthrough said second heat exchanger so as to control the cooling capacityof said second heat exchanger.
 15. The system of claim 14, furthercomprising a means for controlling the operation of said blower so as tocontrol the temperature within said food cart.
 16. The system of claim11, further comprising a means for controlling the operation of saidblower so as to control the temperature within said food cart.
 17. Thesystem of claim 11, further comprising means for controlling said firstpump so as to control the cooling capacity of said second heatexchanger.
 18. The system of claim 14, further comprising means forcontrolling said first pump so as to further control the coolingcapacity of said second heat exchanger.
 19. The system of claim 15,further comprising means for controlling said first pump so as tocontrol the cooling capacity of said second heat exchanger.
 20. Thesystem of claim 19, further comprising a controller for coordinating theoperation of said valve, said first pump and said blower in order tomaintain said food cart at a preselected temperature.
 21. A system forcooling of onboard food carts on aircraft, comprising: a first workingfluid, such first working fluid being in a liquid phase at all times; aplurality of second working fluids; a plurality of first heat exchangersfor transferring heat from said first working fluid to said plurality ofsecond working fluids; a first pump for circulating said first workingfluid through said plurality of first heat exchangers and through fluidconduits to a plurality of second heat exchangers, each such second heatexchanger being associated with a food cart; an expansion tank foraccommodating any expansion or contraction of said first working fluid;a plurality of second pumps for circulating said plurality of secondworking fluids through said plurality of first heat exchangers andthrough fluid conduits to a plurality of third heat exchangers; and aseparate blower for blowing air through each of said second heatexchanger to cool said air and circulate such air within the associatedfood cart.
 22. The system of claim 21, further comprising means forvarying the operation of said first pump to control the circulation rateof said first working fluid and hence the cooling capacity of saidsystem.
 23. The system of claim 22, further comprising a plurality ofvalves, each configured for controlling the flow said first work fluidto one of said second heat exchangers for controlling the coolingcapacity of such second heat exchanger.
 24. The system of claim 21,further comprising a plurality of valves, each configured forcontrolling the flow said first work fluid to one of said second heatexchangers for controlling the cooling capacity of such second heatexchanger.
 25. The system of claim 21, further comprising means forcontrolling the operation of each blower so as to control thetemperature within the associated food cart.
 26. The system of claim 23,further comprising means for controlling the operation of each blower soas to control the temperature within the associated food cart.
 27. Thesystem of claim 24, further comprising means for controlling theoperation of each blower so as to control the temperature within theassociated food cart.
 28. A method for cooling a food cart on anaircraft, comprising: transferring heat from such food cart to acirculating first working fluid, such second working fluid being in aliquid phase at all times; transferring heat from said first workingfluid to a second working fluid; cycling said second working fluidbetween a liquid phase and a gaseous phase; and removing heat from saidsecond working fluid.
 29. The method of claim 28, wherein heat from aplurality of food carts is transferred to said first working fluid. 30.The method of claim 29, wherein heat is transferred to a plurality ofsaid second working fluids and subsequently removed therefrom.
 31. Themethod of claim 30, further comprising varying the flow of said firstfluid to each individual said food cart so as to control the capacity ofsaid first working fluid for having heat transferred thereto from saidindividual food cart.
 32. The method of claim 31, further comprisingvarying the circulation rate of said first working fluid so as tocontrol the overall capacity of said first fluid for having heattransferred thereto.
 33. The method of claim 32, further comprising forcirculating air between an individual food cart and said first workingfluid so as to control the temperature of said individual food cart. 34.A cooling system for aircraft, comprising: means for transferring heatfrom a plurality of food carts to a circulating first working fluid,such first working fluid being in a liquid phase at all times; means fortransferring heat from said first working fluid to a second workingfluid; and means for removing heat from said second working fluid. 35.The cooling system of claim 34, further comprising: means forcontrolling the capacity of said first working fluid for having heattransferred thereto from each food cart individually.
 36. The coolingsystem of claim 35, further comprising means for controlling thecapacity of said first working fluid for having heat transferred fromall food carts collectively.
 37. The cooling system of claim 36, furthercomprising means for controlling the rate of heat transfer to said firstworking fluid from each cart individually.
 38. The cooling system ofclaim 34, further comprising means for controlling the rate of heattransfer to said first working fluid from each cart individually. 39.The cooling system of claim 35, further comprising means for controllingthe rate of heat transfer to said first working fluid from each cartindividually.